Filter

ABSTRACT

A filter, in particular for the separation of leucocytes from further blood components, has an outer sheath, at least one intermediate layer which is a component of a frame or which forms a frame, an inlet chamber which is in communication with an inlet for the medium to be filtered, an outlet chamber which is in communication with an outlet for the filtrate, and a filter material which separates the inlet chamber from the outlet chamber. The filter is particularly low in dead space and can be centrifuged in a simple manner since the filter material is encompassed between the outer sheath and the intermediate layer.

CROSS-REFERENCE TO RELATED APPLICATION

This is a nationalization of PCT/EP03/013596 filed Dec. 2, 2003 andpublished in German.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a filter, in particular for theseparation of leucocytes from further blood components, having an outersheath, having at least one intermediate layer which is a component of aframe or forms a frame, having an inlet chamber which is incommunication with an inlet for the medium to be filtered and an outletchamber which is in communication with an outlet for the filtrate, andhaving a filter material which separates the inlet chamber from theoutlet chamber.

Filters of this kind are, for example, used to liberate blood or bloodcomponents from leucocytes prior to storage or to transfusion to therecipient, since said leucocytes can cause unwanted side effects. Thereis therefore a necessity to separate leucocytes and, optionally, furtherinterfering materials prior to the storage or transfusion of the bloodor of its components (e.g. erythrocites, plasma).

2. Description of the Prior Art

Filters of this kind are known in numerous different embodiments. Thefilter disclosed in EP 0 526 678 B2 has an outer sheath made of flexiblematerial which is connected to an intermediate layer of two soft foilswhich form a frame. The filter material which separates the outletchamber of the filter from the inlet chamber is received in the frame.The filter material is welded into the frame formed by the foils and hasthe effect in this manner that the blood to be filtered or the bloodcomponents to be filtered only have to flow through the filter surfaceto enter into the outlet chamber.

An embodiment of a filter is known from WO 01/91880 A1, wherein theouter sheath consists of two foils which are directly welded to oneanother. No intermediate layer is provided. The filter has in inwardlydisposed welding seam and an outwardly disposed welding seam, with theoutwardly disposed welding seam directly connecting the foils formingthe outer sheath to one another and the inwardly disposed welding seamconnecting the filter material to the outer sheath. A non-welded regioncomprising a filter medium is located between the two welding seams andis resilient due to the lack of a welding seam and damage duringcentrifuging can be largely avoided by means of it. The filter knownfrom WO 01/91880 A1 has the disadvantage that it has stubs on bothoppositely disposed sides of the outer sheath for the inlet of the bloodand for the outlet of the filtrate respectively, whereby a flat surfaceis prevented on both sides of the filter which would be desired for thepurpose of centrifuging.

There is a disadvantage with the filter apparatus known from EP 0 526678 B2 in that dead spaces in which no blood can be filtered arise inthe region of the frame encompassing the filter material. This isunwanted because, on the one hand, the available filter volume is notfully used. On the other hand, there is a disadvantage in that valuableblood components can accumulate in the dead spaces which cannot beregained or can only be regained with difficulty after the end of thefiltration. The accompanying loss of blood components not regained isunwanted.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to further develop afilter of the kind initially named such that it opens up the possibilityof a simple centrifuging and such that the probability for theoccurrence of dead spaces is reduced.

This object is solved by a filter as described herein. Accordingly, thefilter material is encompassed between the outer sheath and theintermediate layer. The advantage is achieved by the connecting of thefilter material to a side of the outer sheath that the occurrence ofdead spaces can be prevented at least on this side and the availablespace of the filter is used correspondingly better. Furthermore, atleast one contact side of the filter can be made without stubs, which isof advantage for the centrifuging.

The advantage further results over the aforesaid EP 0 526 678 B2 due tothe design of the filter in accordance with the invention that thefilter in accordance with the invention can consist of three layers, ofwhich one forms the intermediate layer and two form the outer sheath,whereas the filter disclosed in the named printed document consists ofat least four layers, namely of two intermediate foils to fix the filtermaterial in place and of two layers forming the outer sheath. The filterin accordance with the present invention can generally also have morethan three layers.

The intermediate layer is a component of the frame encompassing thefilter material or forms the frame and has the advantage that, due tothe number of welded layers, the welding seams can be made comparativelysoft, whereby damage during the centrifuging can largely be avoided. Thefilter material extends in the recess formed by the frame.

If the intermediate layer is only a component of a frame, the furtherframe components, i.e. the further sections fixing the filter materialin place or encompassing it, are formed, for example, by the outersheath. In an aspect of the invention of this kind, the arrangement ofthe filter material between the intermediate layer and the outer sheathin accordance with the invention is accordingly only providedregionally. The arrangement of the filter material between theintermediate layer and the outer sheath in accordance with the inventionthus does not have to be present in the whole filter periphery region,but can also only be provided for partial regions, for example for theregion of the outlet.

The shape of the intermediate layer can be any desired one and can beselected freely depending on the existing demands. It is, for example,feasible to design the intermediate layer in the form of a straight orcurved strip, in U shape, in the form of a semi-circle, etc., or also ina peripheral manner, whereby a closed frame is created.

To avoid damage during centrifuging, it is advantageous for the filterto have an outer sheath consisting of flexible material.

The outer sheath can consist of two parts, in particular foils, whichare welded to one another, with the filter material being encompassedbetween one of these parts and the intermediate layer. In a preferredaspect of the invention, the outer sheath and/or the intermediate layerconsist of PVC.

It is particularly advantageous for the filter material to beencompassed between the outer sheath on the inlet side and theintermediate layer.

The filter material can be welded to the outer sheath and to theintermediate layer.

In an advantageous aspect of the invention, the intermediate layerconsists of flexible material.

A first inwardly disposed welding seam can be provided which connectsthe filter material to the intermediate layer and to the outer sheath,and a second outwardly disposed welding seam can be provided whichconnects the intermediate layer to the outer sheath. The inwardlydisposed welding seam fixes the filter material in place in this mannerbetween the intermediate layer and the outer sheath. The outwardlydisposed welding seam connects the intermediate layer to the outersheath.

In an embodiment of this kind, the marginal region of the filtermaterial is preferably arranged in a region which extends between bothwelding seams around the filter material. It is particularlyadvantageous for the intermediate layer to have one or more apertureswhich connect the marginal region of the filter material encompassed inthe frame to the inlet chamber and the outlet chamber. Such aperturesbring along the advantage that no or comparatively little materialremains in this region of the filter material, but flows from thereeither into the outlet chamber or back into the inlet chamber and can befiltered again. The loss of e.g. blood or blood components can beminimized in this manner.

The aperture(s) of the intermediate layer is/are preferably arranged ina region between the first and second welding seams. It can be achievedin this manner that the filtered medium, in particular blood, preferablyflows, starting from this region, into the outlet chamber. With acorresponding design of the apertures, it is likewise possible to guidethe filtered blood back into the inlet chamber and to filter it again.

In accordance with a further aspect of the present invention, aplurality of intermediate layers are provided. In this case, the filterhas four or more layers of which e.g. two form the outer sheath and e.g.two are made as intermediate layers. More than four layers can also beused. The risk of damage during centrifuging is reduced if more layersare welded to one another. The softness and resilience of the weldingseams and thus of the filter can be increased by the number ofintermediate layers.

It is particularly advantageous for the outer sheath to consist of twofoils welded to one another. They can be directly welded to one anotheror can receive one or more intermediate layers between them.

In a further aspect of the present invention, provision is made for thefilter material to be elliptic in its plan view. This aspect permits anoptimum filter utilization by a uniform distribution of blood on thefilter material. Furthermore, the occurrence of dead zones can belargely avoided by an elliptic design.

The inlet for the medium to be filtered, for example for the concentrateof erythrocites, can consist of a stub welded to the outer sheath whichconsists of two limbs arranged at right angles to one another and ofwhich the limb welded to the outer sheath substantially extendsperpendicular from the outer sheath.

The outlet can consist of a cylindrical stub which is welded to theouter sheath and/or to the intermediate layer and whose longitudinalaxis extends in a plane which extends parallel to the plane formed bythe filter material and is offset with respect to it. The outlet stub isthus arranged “asymmetrically”. It can be welded between the outersheath and the intermediate layer or also directly between two foilsforming the outer sheath.

It is particularly advantageous for the filter material to be pressed orneedled. A design of the filter material of this kind reduces the filtervolume with an unchanged filter mass and thus increases the filterdensity. This has the advantage that the stability of the filter mediumis in particular increased during the centrifuging. Furthermore, theregaining of blood from the filter is improved due to the lower volumewith an unchanged filter performance.

Further details and advantages of the present invention will beexplained in more detail with reference to an embodiment shown in thedrawing. There are shown:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: a side view and a plan view of the leucocyte filter inaccordance with the invention;

FIG. 2: a sectional representation in accordance with section line A-Ain FIG. 1;

FIG. 3: an enlarged representation of detail B and detail C in FIG. 2;and

FIG. 4: different representations of a further embodiment of a filter inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

FIG. 1 shows the leucocyte filter 10 in accordance with the invention ina side view. It has an outer sheath consisting of the foils 12, 14. Thefoils 12, 14 are made in flexible form and consist of PVC. The outerfoil 14 is welded to the inlet stub 20 which has two limbs which arearranged at right angles to one another and of which the limb welded tothe foil 14 extends perpendicular thereto, whereas the other limbextends substantially parallel to the outer foil 14.

Furthermore, the outlet stub 30 is provided which is substantiallycylindrical. It is welded to the outer foil 12 and to a foil 16 formingan intermediate layer (see FIG. 3, detail B).

The foils 12, 14 are welded at their periphery to the intermediate layer16, whereby an outwardly disposed welding seam 35 is formed.

As can be seen from FIG. 1, the longitudinal axis of the stub 30 is notlocated in the plane of the welding seam 35, but in a plane whichextends parallel to it and which is offset with respect to the plane ofthe welding seam 35.

It can be seen from the plan view of the leucocyte filter in accordancewith FIG. 1, right hand illustration, that it has an elliptic shape. Theinlet stub 20 is not arranged at the center of the elliptic region,but—in accordance with FIG. 1—above it. The elliptic design of thefilter permits an ideal distribution of the medium to be filtered,whereby the filter is largely utilized. In addition, dead zones can belargely avoided.

FIG. 2 shows the sectional representation of the leucocyte filter inaccordance with the sectional line A-A in FIG. 1. The arrangement of thefilter material 40 can be seen from this which separates the inlet side50, into which the medium to be filtered flows after exiting the inletstub 20, from the outlet side 60, into which the filtrate flows throughthe filter and exits through the stub 30. The filter material 40consists of polybutylene terephthalate fibers which can be coated. Thefilter material 40 can be made in multilayers.

The filter material 40 is a pressed or needled filter element whichshould be indicated in a schematic manner by the recesses 42. A filterelement of this kind has the advantage that its mechanical stability isincreased, which is in particular necessary for the purpose ofcentrifuging. A further advantage consists of the fact that theregaining of the medium located in the filter material is facilitated.The filter performance is not negatively influenced by the reducedvolume of the filter material. The amount of the filter material remainsidentical with respect to a non-pressed or non-needled embodiment.

FIG. 3 shows the details B and C in accordance with FIG. 2. Detail Brelates to the region of the outlet stub 30 which is welded between theouter foil 12 and the intermediate foil 16 welded to the outer foil 14.The outlet stub 30 extends parallel to the longitudinal axis of theelliptically made filter. As can in particular be seen from FIG. 2, theoutlet stub 30 is arranged at the lowest point of the outlet chamber 60so that it can be fully emptied. As can in particular be seen from FIG.2, a substantially flat support of the filter can be formed in thismanner which is formed in the present case by the outer foil 12.

As can likewise be seen from FIG. 2 and detail B in FIG. 3, the centralaxis of the cylindrical outlet stub 30 is not located in the plane whichis formed by the filter material 40, but is made offset thereto.

An enlarged view of the upper end region of the filter 10 can be seenfrom Figure C. The outer foil 14, the filter material 40 and theintermediate foil 16 are shown here which are welded to one another bymeans of a first, inwardly disposed welding seam 37. Furthermore, thesecond, outwardly disposed welding seam 35 can be seen which connectsthe foils 12 and 14 to the intermediate foil 16. The marginal zone ofthe filter material 40 is located between these welding seams. As can beseen from detail C, the intermediate foil 16 has a recess 18 whichconnects the marginal region of the filter material 40 to the outletchamber. It is thereby achieved that blood or blood components can alsobe regained from this marginal region of the filter material 40. As canbe seen from FIG. 3, the filter material 40 is welded between the foil14 forming the outer sheath on the inlet side and the intermediate layer16. The advantage thereby results that the filter is made free of deadspace on the inlet side since the filter material 40 is welded directlyto the outer foil 14, as can also be seen from FIG. 2.

The following example illustrates the influence of the apertures of theintermediate layer in accordance with the invention and the treatment ofthe filter material:

EXAMPLE 1

35 cm² filter area, 26 layers of coated PBT (average diameter 2 μm,surface density 50 g/m²); design of the welding seams in accordance withFIGS. 1-3:

-   WBC (white blood cells): fewer than 200,000/RCC (red cell    concentrate) unit;-   Filtration time: 10-13 minutes;-   RCC yield: 93%.

EXAMPLE 2

The filter corresponds to the filter of Example 1, but in thenon-needled or pressed state of the filter material;

-   WBC: 200,000-400,000;-   Filtration time: 15-17 minutes;-   RCC yield: 89%.

EXAMPLE 3

The filter corresponds to the filter of Example 1, but without aperturesof the intermediate layer;

-   WBC: fewer than 200,000/RCC unit;-   Filtration time: 10-13 minutes;-   RCC yield: 91%.

FIG. 4 shows a further embodiment of the present invention in differentviews in which the joining of the marginal region of the filter materialto the intermediate layer is shown in simplified form.

In the embodiment in accordance with FIG. 4, two filter media 40′arranged in series are provided. They are welded in their marginalregions to a foil 16′ made as an intermediate layer. The foil 16′ isfurthermore welded to the foils 12′ and 14′ which form the outer sheathof the filter.

The medium to be filtered flows through the inlet stub 90 which is alsocylindrical like the outlet stub 100 and first flows through the filtermaterial 40′ shown on the right from the bottom to the top. From there,the medium is guided through corresponding recesses on the upper side ofthe filter material 40′ arranged on the left hand side, flows through itand is finally removed through the outlet stub 100.

The foils 12′, 14′ forming the outer sheaths and also the foil 16′forming the intermediate layer are made of PVC.

The filter shown in FIG. 4 is symmetrical and can be folded about acentral axis, as is reproduced in FIG. 4, lower illustration. In thisstate, the filter can be centrifuged particularly advantageously.

The invention being thus described, it will be apparent that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be recognized by one skilled in the art areintended to be included within the scope of the following claims.

1. A filter, in particular for the separation of leucocytes from furtherblood components, comprising an outer sheath, at least one intermediatelayer which is a component of a frame or which forms a frame, an inletchamber in communication with an inlet for a medium to be filtered, anoutlet chamber in communication with an outlet for a filtrate, a filtermaterial which separates the inlet chamber from the outlet chamber andwhich is encompassed between the outer sheath and the intermediatelayer, a first inwardly disposed welding seam which connects the filtermaterial to the intermediate layer and to the outer sheath, and a secondoutwardly disposed welding seam which connects the intermediate layer tothe outer sheath.
 2. The filter in accordance with claim 1, wherein theouter sheath is made of flexible material.
 3. The filter in accordancewith claim 1, wherein the outer sheath comprises a first foil and asecond foil welded to one another, and wherein the filter material isencompassed between one of the foils and the intermediate layer.
 4. Thefilter in accordance with claim 1, wherein the filter material isencompassed between the outer sheath on an inlet side and theintermediate layer.
 5. The filter in accordance with claim 1, whereinthe filter material is welded to the outer sheath and to theintermediate layer.
 6. The filter in accordance with claim 1, whereinthe intermediate layer is constructed of flexible material.
 7. Thefilter in accordance with claim 1, wherein the intermediate layer hasone or more apertures which connect a region of the filter materialencompassed in the frame to at least one of the inlet chamber and theoutlet chamber.
 8. The filter in accordance with claim 7, wherein theapertures are arranged in a region between the first and second weldingseams.
 9. The filter in accordance with claim 1, wherein a plurality ofintermediate layers are provided.
 10. The filter in accordance withclaim 1, wherein the filter material is elliptic in shape in plan view.11. The filter in accordance with claim 1, wherein the inlet includes astub which is welded to the outer sheath and which has a first limb anda second limb arranged at right angles to one another, with the limbwelded to the outer sheath extending substantially perpendicular fromthe outer sheath.
 12. The filter in accordance with claim 1, wherein theoutlet includes a cylindrical stub which is welded to at least one ofthe outer sheath and the intermediate layer and which has a longitudinalaxis extending in a plane parallel to a plane formed by the filtermaterial and being offset with respect to the plane of the filtermaterial.
 13. The filter in accordance with claim 1, wherein the filtermaterial is pressed.
 14. The filter in accordance with claim 1, whereinthe filter material is needled.